please see this link: http://build.sharpdevelop.net/buildartefacts/#SD45
i don't think they have published .net 4.5 yet, have they?
That's just a branch in preparation so that we can get started as soon as we get the .NET 4.5 bits (I think that there will be a beta release published at the Build conference).
But at the moment, that branch is not using .NET 4.5 yet; it's identical to 4.2 (except for the version number).
async
/await
support for code completion is already on the 4.2 branch.